It has been used for many years to dye the hair to cover appearing grey hair. The need to do so arises from the fact that grey hair is the first sign of having past adolescence, which can be hard to accept for many people.
For instance, in certain parts of Asia it is widely used by both men and women to dye the hair with dyes often referred to by humorous people as "black shoe polish".
During the last few decades hair dyeing has become more and more popular in the western world. At first Punk Rockers and other society critical groups dyed their hair in extreme colours as a part of their protest against the established society, but today especially many young people also uses hair dyes (in more soft tints than the Punk Rockers) as a sort of "cosmetic" to change or freshen up their "look".
Hair dyes
In general hair dyeing compositions on the market today can be divided into three main groups:
temporary hair dyes, PA0 semi-permanent hair dyes, and PA0 permanent oxidative hair dyes.
The temporary hair dyes are only intended to change the natural hair colour for a short period of time and usually functions by depositing dyes on the surface of the hair. Such hair dyes are easy to remove with normal shampooing.
When using semi-permanent hair dyes the colour of the dyed hair can survive for five or more shampooings. This is achieved by using dyes having a high affinity for hair keratin and which is able penetrate into the interior of the hair shaft.
Permanent hair dyes are very durable to sunlight, shampooing and other hair treatments and need only to be refreshed once a month as new hair grows out. With these dyeing systems the dyes are created directly in and on the hair. Small aromatic colourless dye precursors (e.g. p-phenylene-diamine and o-aminophenol) penetrate deep into the hair where said dye precursors are oxidised by an oxidising agent into coloured polymeric compounds. These coloured compounds are larger than the dye precursors and can not be washed out of the hair.
By including compounds referred to as modifiers (or couplers) in the hair dyeing composition a number of hair colour tints can be obtained. Cathecol and Resorcinol are examples of such modifiers.
Traditionally H.sub.2 O.sub.2 is used as the oxidizing agent (colour builder), but also as a bleaching agent. Dyeing compositions comprising H.sub.2 O.sub.2 are often referred to as "lightening dyes" due to this lightening effect of H.sub.2 O.sub.2.
The use of H.sub.2 O.sub.2 in dyeing compositions have some disadvantages as H.sub.2 O.sub.2 damages the hair. Further, oxidative dyeing often demands high pH (normally around pH 9-10), which also inflicts damage on the hair and on the skin. Consequently, if using dye compositions comprising H.sub.2 O.sub.2 it is not recommendable to dye the hair often. To overcome the disadvantages of using H.sub.2 O.sub.2 it has been suggested to use oxidation enzymes to replace H.sub.2 O.sub.2.
U.S. Pat. No. 3,251,742 (Revlon) describes a method for dyeing human hair by dye formation in situ (i.e. on the hair). An oxidative enzyme is used to the colour formation reactions at a substantially neutral pH (7-8.5). Laccases, tyrosinases, polyphenolases and catacolases are mentioned as suitable oxidation enzymes. The only exemplified oxidation enzyme is tyrosinase.
EP patent no. 504.005 (Perma S.A.) concerns dyeing compositions for keratinous fibres, in particular hair, which do not require the presence of H.sub.2 O.sub.2 (hydrogen peroxide). The composition comprises an enzyme capable of catalysing the formation of the polymeric dyes and also dye precursors, such as bases and couplers, in a buffer solution wherein the pH of said composition is between 6.5 and 8 and said enzyme has an optimal activity in the pH range between 6.5 and 8.
Rhizoctonia praticola laccase and Rhus vernicifera laccase are the only laccases exemplified in the patent.
Abstract of Papers American Chemical Society vol. 209, no. 1-2, 1995 discloses the cloning of laccases from Scytalidium thermophilum and Myceliophthora thermophila. The abstract does not mention the use of said laccases for dyeing.